Bond Angle Disorder in Tetrahedrally Bonded Amorphous Silicon

Abstract

ABSTRACTThere have been many studies of the vibrational and optical properties of a- Si and a-Ge that have correlated systematic variations of these properties with films grown and/or annealing temperatures, and have attributed these variations to changes the local atomic structure and intrinsic network disorder that are correlated with the thermal history of a particular sample. The most frequently proposed atomic structure parameter associated with this intrinsic disorder has been the width of the bond angle distribution. We attempted to isolate the effects of bond angle disorder on the vibrational and electronic properties of a-Si using a Bethe Lattice structure that avoids some of the uncertainties introduced by the uncontrolled variation in other atom structure parameters. Using this approach, we show that increases in the width of the bond angle distribution can account for trends in the calculated vibrational and optical properties wth thermal hisrory that are in good qualitative agreement with trends reported in the experiments.